Matthew 2:16ὅτι
When Herod saw that he had been outwitted by the Magi, he was filled with rage. Sending orders, he put to death all the boys in Bethlehem and its vicinity who were two years old and under, according to the time he had learned from the Magi.
Mark 1:15ὅτι
“The time is fulfilled,” He said, “and the kingdom of God is near. Repent and believe in the gospel!”
Luke 1:22ὅτι
When he came out and was unable to speak to them, they realized he had seen a vision in the temple. He kept making signs to them but remained unable to speak.
John 1:15ὅτι
John testified concerning Him. He cried out, saying, “This is He of whom I said, ‘He who comes after me has surpassed me because He was before me.’”
Acts 1:5ὅτι
For John baptized with water, but in a few days you will be baptized with the Holy Spirit.”
1 John 1:5ὅτι
And this is the message we have heard from Him and announce to you: God is light, and in Him there is no darkness at all.

Abbott-Smith

ὅτι,
conjc. (prop. neut. of ὅστις).

I. As conjc, introducing an objective clause, that;

1. after verbs of seeing, knowing, thinking, saying, feeling: Mat.3:9 6:32 11:25, Mrk.3:28, Luk.2:49, Jhn.2:22, Act.4:13, Rom.1:13 8:38 10:9, Php.4:15, Jas.2:24, al.; elliptically, Jhn.6:46, Php.3:12, al.

2. After εἶναι (γίνεσθαι): defining a demonstr. or of person(s) pron., Jhn.3:19 16:19, Rom.9:6, 1Jn.3:16 al.; with pron. interrog., Mat.8:27, Mrk.4:41, Luk.4:36, Jhn.4:22 al.; id. elliptically, Luk.2:49, Act.5:4, 9, al.;

3. Untranslatable, before direct discourse (ὅτι recitantis): Mat.7:23, Mrk.2:16, Luk.1:61, Jhn.1:20, Act.15:1, Heb.11:18, al. (on the pleonastic ὡς ὅτι, see: ὡς).

II. As causal particle, for that, because: Mat.5:4-12, Luk.6:20, 21, J0 1:30 5:27, Act.1:5, 1Jn.4:18, Rev.3:10, al. mult.; διὰ τοῦτο ὅτι, Jhn.8:47 10:17, al.; answering a question (διὰ τί), Rom.9:32, al.; οὐκ ὅτι . . . ἀλλ᾽ ὅτι, Jhn.6:26 12:6.
(AS)

Sources: Abbott-Smith’s Manual Greek Lexicon of the New Testament (1922, public domain) and glosses from STEPBible TBESG (CC BY 4.0); STEPBible TAGNT (Greek New Testament, CC BY 4.0); the Berean Standard Bible (public domain). Reformatted by Word Study, wording unchanged. All sources and licenses.